function T = Eci2Ecef(UTC)
    
    Tu = JulianDate(UTC) - 2451545;
    %[solar days]Solar days that have passed between the current UTC and January 1, 2000 at noon.
    
    ERA = 2 * pi * (0.7790572732640 + 1.00273781191135448 * Tu);
    %[rad]Current Earth rotation angle.
    
    T = [ cos(ERA), sin(ERA), 0; ...
         -sin(ERA), cos(ERA), 0; ...
                 0,        0, 1];
    %[]Transformation matrix that transforms vectors from ECI to ECEF.
    
end
%===================================================================================================